Production of ducted articles



Nov. 7, 1961 N. w. GORDON ETA!- 3,007,794

PRODUCTION OF DUCTED ARTICLES Filed Aug. 11, 1958 F Fig .1

I III V 'I l l fif- L 5 v I) Q Q 7 7 INVENTOES NORMAN W/LdiON GORDON IAN ALEX/N551? WHITE A TTORNE Y6 nitcd 3,007,794 PRODUCTION OF DUCTED ARTICLES Norman Wilson Gordon and Ian Alexander White, Birmingham, England, assignors to The Birmingham Small Arms Company Limited, Birmingham, England,

a British company 7 Filed Aug. 11, 1958, Ser. No. 754,401 Claims priority, application Great Britain Aug. 15, 1957 8 Claims. (Cl. 75214) This invention relates to the production of ducted articles and has particular but not exclusive reference to that kind of ducted article which is intended for use at high temperatures under high loading, for example ducted blades wherein the ducts serve for the passage therethrough of fluid for cooling the blades.

In the production of ducted articles such as ducted turbine blades, it has been proposed to employ ductforming elements which serve to form the ducts in the article but which, with certain exceptions, require to be removed or dispersed after formation of the article so as to leave the required ducts. The duct-forming elements most easily removable are those which are made from material which is volatilizable at ordinary sintering temperatures, for example, cadmium or zinc wire, but these sufier from the disadvantage of not having sufiicient strength and rigidity to be able to stand up to the treatment which they undergo during the formation of the article, without sufiering excessive deformation. Material such as copper wire has just sufiicient strength and rigidity to stand up to the said treatment, but has to be removed by melting and dispersing into the pores or voids of the body of the article. This may be disadvantageous in that desirable properties of the article, particularly at high temperatures, may be adversely affected by the pres ence of the dispersed material. Strong and rigid material such as steel wire or rod is greatly to be desired from the point of view of withstanding the said treatment, but it is difficult to remove and cannot be dispersed by melting at the temperatures normally employed for sintering.

According to the invention, for use in the production of ducted articles wherein the articles are formed around duct-forming elements which are subsequently removed to leave the required ducts, a duct-forming element has a core of strong and rigid material normally difiicult to disperse or remove after formation of the article, the core being coated with material readily capable of being dispersed or removed so as to leave sufficient clearance between the said core and the surrounding material of the formed article to enable the core to be Withdrawn from the formed article and thereby leave a duct therein.

The said coating may be applied to the core by dipping or plating. Plating may be accomplished by electrodeposition, mechanical, chemical or any other suitable means.

In order that the invention may be clearly understood and readily carried into practice, reference is now made to the appended illustrative drawings, wherein:

FIGURE 1 is a plan view of a pair of supports having duct-forming elements mounted therein as an assembly for incorporation in a die cavity for the production of a ducted article.

FIGURE 2 is an end view of FIGURE 1, and

FIGURE 3 is a similar view to FIGURE 2 showing the duct-forming elements as ready for removal after formation of a ducted article.

Referring to the drawings, which illustrate by way of example means for performing a method of production of a ducted turbine blade from powder metal, supports 1 preferably made from copper plate have a number of apertures therein adapted to engage the ends of wires 3 cut into equal lengths corresponding to the length of the die employed in the production of the turbine blade, the number of wires used corresponding to the number of ducts required in the finished turbine blade.

Each wire 3 preferably consists of a core of steel Wire of 14 S.W.G. (:080" diameter) to which is applied a relatively thin coating of a volatilizable material such as zinc or cadmium which is capable of readily being dispersed or removed from the steel core wire. The coating 5 may be produced by dipping the steel core 3 into a bath of molten zinc until the required thickness has been built up, such coating being .012 in thickness so that each ductforming element having a core diameter of .080" is .104" (12 S.W.G.) in total diameter after coating, as determined by the employment of a suitable gauge; Instead of applying the coating material to the core wire by dipping, such could be applied by plating of the core wire, which may be accomplished by known methods such for example as electro or chemical deposition.

The assembly, as seen in FIGURE 2, is as it appears when placed in a die cavity in which metal powder is compacted and subsequently pre-sintered preferably under vacuum or by using an inert gas (e.g. Ar) or reducing gas (pure dry H During the pre-sintering the coating 5 distils and is removed as vapour, leaving the 14 S.W.G. steel core wires 3 in holes of a diameter equivalent to about the total diameter of the Wires after coating (Le. 12 S.W.G.) as seen in FIGURE 3, both dimensions being less such amount of compressing of coating and core as may have taken place during compacting. After presintering, the compact is allowed to cool and the steel wire 3 can readily be withdrawn because of the clearance 7 produced by the removal of the coating 5, leaving the required ducts in the turbine blade compact, which is then sintered.

Where the coating of the core Wires 3 is of a material other than zinc, for example copper, capable of becoming molten at temperatures usually employed in the formation of the ducted article, for example in sintering, the coating can be dispersed by causing it to melt and flow and occupy pores or voids in the surrounding material. It will be appreciated that as only a relatively thin coating, for example .012" on a core of diameter .080 is required, the amount of dispersed material is small compared with the amount which would have to be dispersed were the duct-forming element formed completely of that material, and therefore adverse affecting of the desirable properties of the ducted article due to the presence of the dispersed material would be correspondingly reduced. However, where merely a trace of such material would adversely affect the desirable properties by too great an amount, as may be the articles formed from alloys having high creep resistance at high temperatures, dispersing is best avoided and a material capable of being removed rather than dispersed is advantageously employed.

The term fluidized as used in the claims includes dispersal of the core coacting material by volatilization, evaporation, melting or any equivalent manner.

It will be appreciated that the core wire and its coating could be produced as a composite article by casting the removable or dispersable material on to the core wire, the composite article being subjected if necessary to a drawing operation to reduce the thickness of the removable or dispersable material to the required amount.

We claim:

1. A method of producing ducted powdered metal articles by compacting and sintering which comprises compacting powdered metal into required shape with duct-forming cores distributed through said powdered metal where the ducts are desired, coating said cores thinly with a metal which fluidizes at ordinary sintering temperatures for the powdered metal, said cores being Patented Nov. 7., 1961- made of relatively rigid ferrous material which does not melt at said ordinary sintering temperatures and subjecting the compacted assembly to sintering temperatures so that said thin coatings flow away from about said cores leaving duct defining clearance spaces between the cores and powdered metal to enable 'said cores to be withdrawn completely from the spaces so as to provide essentially unobstructed ducts in said article.

2. The method of producing ducted articles according 7 copper.

6, The method of producing ducted articles according to claim11 wherein said core coating metal is volatilizable at'said sintering temperatures.

.7. The method of producing'ducted articles according to claim 1 wherein said core coating metal melts to fluent,

condition atsaid sintering temperatures.

'8 The process of makinga ducted powdered metal article by compacting and s'intering which comprises the steps of compacting powdered 'metal into required shape with ferrous metal core .wires distributed through said powdered metal where the; ductsrare desired, said core Wires each being coated thinly. with a fusible metal which fluidizes at ordinary sintering.temperaturesfor the powdered metal and said core wires being made of material which does not melt at said ordinary sintering temperatures, subjecting the compacted assembly to sintering temperatures for the powdered me'talso that said thin a coatings flowi'a'way from about said wires leaving duct defining clearance spaces between the wires and'powdered' metal, andlongitudinally Withdrawing said'wires com- 'pletely from'the spaces so as to provide essentially unobstructed ducts in said article. V

References Cited in the file at this patent UNITED STATES PATENTS 2,628,166." {Hana 'Feb'. 10, 1953 22,751,293 Haller June '19, 1956 j 7 

1. A METHOD OF PRODUCING DUCTED POWDERED METAL ARTICLES BY COMPACTING AND SINTERING WHICH COMPRISES COMPACTING POWDERED METAL INTO REQUIRED SHAPE WITH DUCT-FORMING CORES DISTRIBUTED THROUGH SAID POWDERED METAL WHERE THE DUCTS ARE DESIRED, COATING SAID CORES THINLY WITH A METAL WHICH FLUIDIZES AT ORDINARY SINTERING TEMPERATURES FOR THE POWDERED METAL, SAID CORES BEING MADE OF RELATIVELY RIGID FERROUS MATERIAL WHICH DOES NOT MELT AT SAID ORDINARY SINTERING TEMPERATURES AND SUBJECTING THE COMPACTED ASSEMBLY TO SINTERING TEMPERATURES SO THAT SAID THIN COATINGS FLOW AWAY FROM ABOUT SAID CORES LEAVING DUCT DEFINING CLEARANCE SPACES BETWEEN THE CORES AND POWDERED METAL TO ENABLE SAID CORES TO BE WITHDRAWN COMPLETELY FROM THE SPACES SO AS TO PROVIDE ESSENTIALLY UNOBSTRUCTED DUCTS IN SAID ARTICLE. 